[Info-vax] OpenVMS - file selection abnormally with Copy / Rename or user ignorance?

[David Froble]

JF Mezei wrote:
> On 15-03-28 16:36, Stephen Hoffman wrote:
> 
>> AFAIK, the circumstances are not officially documented.
>> This because there's no upside to discussing the details.
> 
> I declare that satisfying JF's curiosity to be an "upside". Therefore
> the above statement is false. :-)


Ok

> 
>>         Also, all cases in which these data corruptions can occur
>>         in the data that BACKUP transfers are not reliably reported
>>         to you;
> 
> Are there cases where BACKUP/IGNORE would NOT report a file as currently
> opened at the time BACKUP begins to copy a file ?

No, if the file is open, BACKUP will report that fact.  Also, consider, 
the /IGNORE=INTERLOCK is to allow BACKUP to OPEN the file.  Once the 
file is open, things are different.  If other writes occur, BACKUP is 
unaware, and, frankly, doesn't care.  It's doing what it needs to do. 
Or, should I say, what it's been TOLD to do.

I've never tried it, but, I'm betting that once BACKUP has a file open, 
others cannot open it.

> 
> 
> And in terms of problems, instead of "corruption" isn't it more correct
> to state "unpredictable data" ?

Well, as corrupt data is unpredictable, that's Ok to say.  But, true 
corruption is possible.  Consider a keyed file.  The data is written 
after BACKUP has copied that part of the file, but, not yet copied the 
secondary keys.  So, it's going to have a secondary key, or keys, 
pointing to perhaps a record not in the BACKUP save set.  I'd call that 
corruption.  And all that's before considering transactions written to 
multiple files as a single transaction.  That's when it gets bad.


> From a true "corruption" point of view, would the only corruption
> possible be an indexed file where bucket split and new records added
> after BACKUP has already copied the index blocks , and ends up copying
> the new data buckets ?
> 
> From a sequential or relative file point of view, wouldn't file
> integrity remain , but new data may or may not be copied ?
> (unpredictable). ?

It's transactions that really matter.